It is known that many of the known antibiotic substances which are produced by the cultivation of different kinds of microorganisms can exhibit an anticancer or antitumor activity. Up to date, some of the known anticancer antibiotic or antitumor antibiotic substances have extensively been used as a chemotherapeutic anticancer or antitumor agent and provide an important mean for therapeutic treatment of cancers or tumors in the clinic practice. However, many of the known anticancer antibiotic substances which have been used in the clinic practice can exhibit considerable toxicity to human body so that the practical use of them is greatly limited. In this sense, all the known anticancer antibiotics which have been used in the clinic practice are not necessarily a completely satisfactory anticancer agent or antitumor agent. Accordingly, there now remains an outstanding demand to discover and provide such novel substances that have a low toxicity to human but a high anticancer or antitumor activity and that can be effectively and safely used for the therapeutic treatment of a cancer or tumor in human patients. An object of this invention is to provide a new antibiotic substance which is useful as an anticancer agent or antitumor agent having the above-mentioned desirable properties. Another object of this invention is to provide a new anticancer antibiotic, now nominated as MI43-37F11 substance, which is utilizable as the anticancer or cancerocidal agent or as the antitumor agent having the above-mentioned desirable properties in the clinic practice. A further object of this invention is to provide a process for the fermentative production of the new anticancer antibiotic, MI43-37F11 substance. Still another objects of this invention will be clear from the following descriptions.
Thus, we, the present inventors, have made extensive researches in an attempt to discover and provide a new anticancer antibiotic substance, and we have now succeeded in obtaining a new anticancer antibiotic, now nominated as MI43-37F11 substance, and having the following formula [I]: ##STR2## from the culture of a certain new microbial strain, and have found that this MI43-37F11 substance exhibits a highly useful anticancer activity without showing any observable toxicity to mammalian. We have now thus accomplished this invention.